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USGS Mineral Resources Program The Rare-Earth Elements— Vital to Modern Technologies and Lifestyles

Until recently, the rare-earth elements (REEs) were familiar to a relatively As part of a broad mission to conduct research small number of people, such as chemists, geologists, specialized materials and provide information on nonfuel mineral scientists, and engineers. In the 21st century, the REEs have gained visibility resources, the U.S. Geological Survey (USGS) through many media outlets because (1) the public has recognized the critical, supports science to understand the following: specialized properties that REEs contribute to modern technology, as well as (2) China’s dominance in production and supply of the REEs and (3) inter­ • Where and how concentrations of rare- national dependence on China for the majority of the world’s REE supply. earth elements form in the Earth’s crust; Since the late 1990s, China has provided 85 – 95 percent of the world’s • Where undiscovered/undeveloped resources REEs. In 2010, China announced their intention to reduce REE exports. During of rare-earth elements may occur; this timeframe, REE use increased substantially. REEs are used as components in high technology devices, including smart phones, digital cameras, computer • Trends in the supply and demand of hard disks, fluorescent and light-emitting-diode (LED) lights, flat screen rare-earth elements domestically and televisions, computer monitors, and electronic displays. Large quantities of internationally; some REEs are used in clean energy and defense technologies. Because of the many important uses of REEs, nations dependent on new technologies, • How undisturbed and mined rare-earth such as Japan, the United States, and members of the European Union, reacted deposits interact with the environment. with great concern to China’s intent to reduce its REE exports. Consequently, exploration activities intent on discovering economic deposits of REEs and bringing them into production have increased. List of the rare-earth elements found in natural deposits—the “” plus . [Average abundance (concentration) in the earth’s crust What are the Rare-Earth Elements? (in parts per million) from Lide (2004, CRC handbook The REE is composed of 15 elements that range in of physics and chemistry, 85th edition). For comparison, from 57 () to 71 () on the of elements, and are average crustal abundances for , , , and copper are 0.004, 0.075, 14, and 60 parts per million, officially referred to as the “lanthanoids,” although they are commonly referred respectively] to as the “lanthanides.” The rare-earth element promethium (atomic number 61) is not included in discussions of REE deposits because the element is rare and Atomic Crustal Element Symbol unstable in nature. Yttrium (atomic number 39) is commonly regarded as an number abundance REE because of its chemical and physical similarities and affinities with the Light REEs lanthanoids, and yttrium typically occurs in the same deposits as REEs. Lanthanum La 57 39 (atomic number 21) is chemically similar to, and thus sometimes included with, the Ce 58 66.5 REEs, but it does not occur in economic concentrations in the same geological Pr 59 9.2 settings as the lanthanoids and yttrium and will not be discussed further. Nd 60 41.5 Traditionally, the REEs are divided into two groups on the basis of atomic Sm 62 7.05 weight: (1) the light REEs are lanthanum through gadolinium (atomic numbers 57 through 64); and (2) the heavy REEs comprise terbium through lutetium Europium Eu 63 2.0 (atomic numbers 65 through 71). [Note: Some authorities include europium and Gadolinium Gd 64 6.2 gadolinium within the group of heavy REEs.] Yttrium, although light (atomic Heavy REEs number 39), is included with the heavy REE group because of its similar Terbium Tb 65 1.2 chemical and physical properties. Dysprosium Dy 66 5.2 Most REEs are not as rare as the group’s name suggests. They were named Holmium Ho 67 1.3 “rare-earth elements” because most were identified during the 18th and 19th Erbium Er 68 3.5 centuries as “earths” (originally defined as materials that could not be changed Tm 69 0.52 further by heat) and in comparison to other “earths,” such as lime or magnesia, they were relatively rare. Cerium is the most abundant REE, and is more common Yb 70 3.2 in the Earth’s crust than copper or lead. All of the REEs, except promethium, Lutetium Lu 71 0.8 are more abundant on average in the Earth’s crust than silver, gold, or platinum. Yttrium Y 39 33 However, concentrated and economically minable deposits of REEs are unusual.

U.S. Department of the Interior Fact Sheet 2014 –3078 U.S. Geological Survey November 2014 How Do We Use the Rare-Earth Elements? Did you know.... Due to their unusual physical and chemical properties, such as unique magnetic and optical properties, REEs have Rare-earth magnets are stronger per unit weight diverse applications that touch many aspects of modern life and and volume than any other magnet type. Clean energy culture. Specific REEs are used individually or in combination technologies, such as large wind turbines and electric to make phosphors—substances that emit luminescence—for vehicles, use rare-earth permanent magnets (meaning many types of ray tubes and flat panel displays, in screens that permanently magnetized) that usually contain four REEs: praseodymium, neodymium, samarium, and dysprosium. range in size from smart phone displays to stadium scoreboards. Some REEs are used in fluorescent and LED lighting. Yttrium, europium, and terbium phosphors are the red-green-blue phosphors used in many light bulbs, panels, and televisions. rare-earth magnet. These magnets are also used in a variety of The glass industry is the largest consumer of REE raw conventional automotive subsystems, such as power steering, materials, using them for glass polishing and as additives that electric windows, power seats, and audio speakers. provide color and special optical properties. Lanthanum makes Nickel- hydride batteries are built with lanthanum- up as much as 50 percent of digital camera lenses, including based alloys as anodes. These battery types, when used in cell phone cameras. hybrid electric cars, contain significant amounts of lanthanum, Lanthanum-based catalysts are used to refine . requiring as much as 10 to 15 kilograms per electric vehicle. Cerium-based catalysts are used in automotive catalytic converters. Cerium, lanthanum, neodymium, and praseodymium, Magnets that employ REEs are rapidly growing in commonly in the form of a mixed known as , application. Neodymium-iron-boron magnets are the strongest are used in steel making to remove impurities and in the magnets known, useful when space and weight are limiting production of special alloys. factors. Rare-earth magnets are used in computer hard disks and The end use applications of REEs are detailed in USGS CD–ROM and DVD disk drives. The spindle of a disk drive Scientific Investigations Report 2011–5094 (available at attains high stability in its spinning motion when driven by a http://pubs.usgs.gov/sir/2011/5094/).

Rare-earth elements (REEs) are used in the components of many devices used daily in our modern society, such as: the screens of smart phones, computers, and flat panel televisions; the motors of computer drives; batteries of hybrid and electric cars; and new generation light bulbs. Lanthanum-based catalysts are employed in petroleum refining. Large wind turbines use generators that contain strong permanent magnets composed of neodymium-iron-boron. Photographs used with permission from PHOTOS.com. Where Do Rare-Earth Elements Come From? sodium, potassium, and calcium. Many current (2014) advanced exploration projects are focused on large bodies of alkaline The REEs are commonly found together in the Earth’s igneous rocks, with some finding significant REE concentrations­ +3 crust because they share a trivalent charge ( ) and similar ionic (0.3 –2.6 percent total REE oxide). These deposit types are sought radii. In nature, REEs do not exist individually, like gold or because they are often enriched in the important heavy REEs. copper often do, but instead occur in minerals as either minor Ion-adsorption clay deposits in southern China are the or major constituents.­ In general, these minerals tend to be world’s primary source of heavy REEs. This deposit type is dominated by either light or heavy REEs, although each can informally referred to as “south China clays.” Thick clay accu- be present. In igneous (magmatic) systems, the large sizes of mulations that host low concentrations of REEs (from about the REE ions impede their ability to fit into the structure of 0.04 to 0.25 percent total REE ) form in tropical regions common rock-forming minerals. As a result, when common with moderate to high rainfall through successive processes: silicate minerals crystallize — such as feldspars, pyroxenes, 1. REEs are leached by groundwater from granite bedrock; olivine, and amphiboles— most REEs tend to remain in the coexisting magma. Successive generations of this process 2. thick zones of clay-rich soils develop above the granites; and increase REE concentrations in the residual magma until 3. mobilized REEs become weakly fixed (by ion-adsorption) individual REE minerals crystalize. The REEs can substitute for onto clays in the soils. one another in crystal structures, and multiple REEs typically Despite their low concentrations in REEs, the clay deposits occur within a single mineral. of south China are economic because the REEs can be easily REEs generally occur in uncommon geologic rock types extracted from the clays with weak acids, the deposits are often and settings. As mentioned earlier, REEs are common in the enriched in high-value heavy REEs, and labor costs are low. Earth’s crust but rarely in economic concentrations. Economic A pilot project in Jamaica is evaluating the recovery REE deposits occur primarily in four geologic environments: of REEs from tailings of red mud produced by bauxite carbonatites, alkaline igneous systems, ion-absorption clay (aluminum ore) mining, which could be considered a form deposits, and -xenotime-bearing placer deposits. Even of ion-adsorption clay deposit. within these deposit types, minable (economic) concentrations Monazite-xenotime-bearing placer deposits were impor- of REEs are rare. For example, globally there are more than tant REE sources prior to the mid-1960s. From some modern 500 known carbonatites but only 6 are currently mined for REEs. and ancient beach deposits, the REE-- mineral Other deposit types can contain minor amounts of REEs monazite [(REEs,Th)PO )] can be recovered as a by-product but have not been important REE sources thus far. One example 4 during the extraction of the targeted heavy minerals, ilmenite is the giant Olympic Dam iron oxide-copper-uranium-gold- (FeTiO ), rutile (TiO ), and zircon (ZrSiO ). Ilmenite and silver deposit in Australia, the world’s largest single uranium 3 2 4 rutile —the principal minerals of value as in these deposits—are deposit, which also contains REE enrichments. So far it has not mechanically separated from sand-silt deposits. Monazite can proven economical to recover REEs from this deposit. be recovered simultaneously if desired. The separated ilmenite Carbonatites host the world’s largest REE deposits and and rutile are then chemically processed to remove titanium; are typically most enriched in the light REEs. Carbonatites are ilmenite and rutile are the primary source of the titanium used unusual igneous rocks derived from carbonate-rich magmas, in in paint pigments. Monazite is recovered as a byproduct mineral contrast to the more common silica-rich magmas. Carbonatites from beach sands along the southern coasts of India, where it are igneous rocks with more than 50 percent carbonate minerals, is sought as a source of light REEs and thorium. The recovered usually calcite and dolomite. As a group, carbonatites have the thorium is stockpiled for future use as fuel material in thorium- highest REE concentrations of all igneous rocks. Carbonatites based nuclear power, which is under development. Xenotime have been the world’s main source for light REEs since the (YPO ), a less common mineral, has been recovered as a source 1960s. Currently, REEs are mined from large carbonatite 4 of yttrium and other REEs as a byproduct of mining tin placers. bodies in California (Mountain Pass) and in China (Bayan Obo, Maoniuping, Daluxiang, and Weishan). The Mount Weld mine in Western Australia, Australia, produces REEs from a weathered zone that overlies a carbonatite. Alkaline igneous rocks comprise a group of uncommon igneous rock types generally deficient in silica, relative to

The mineral bastnäsite is an important source of the REEs. Bastnäsite, a REE- carbonate- mineral, is the primary ore mineral in the world’s largest REE deposits. Photograph courtesy of Rob Lavinsky, The mineral monazite is an important source of the REEs. www.iRocks.com. Monazite, a REE-thorium-phosphate mineral, has been separated from some ancient and modern beach sands as a coproduct to the recovery of economic titanium (Ti) minerals. Photograph courtesy of www.geology.com. Worldwide Supply and Demand for Rare-Earth Elements As noted earlier, in recent years Chinese production has accounted for about 95 percent of the REE global market. Citing a need to retain their limited REE resources for domestic requirements and concerns for environmental effects of mining, China has restricted the supply of REEs through quotas, licenses, and taxes. As a result, the REE industry outside of China increased REE stockpiling, explored for deposits in many locations, and promoted new efforts to conserve, recycle, and find substitutes for REEs. New mine production has begun in Australia (Mount Weld) and the United States (Mountain Pass, California). In recent years, expert panels convened by research institutes and government agencies highlighted specific REEs as raw materials critical to evolving technologies, such as clean-energy applications, high-tech military The Mountain Pass mine of Molycorp, Inc., southeastern components, and electronics (Long and others, 2010). These reports suggest California, is the only active producer of REEs in the United that a high potential exists for disruptions in REE supplies. As a result, States (2014). The ore body is a carbonatite intrusion, several expert panel analyses rank REEs high on the “criticality” factor of thought to be the largest REE resource in the United States. raw materials, meaning they are of high technological and economic impor- tance and have high supply-side risk (National Research Council, 2008). Panels and agencies that assessed the criticality of REEs and other raw materials include the National Research Council, U.S. Department of Energy, European Commission, American Physical Society (APS) and Materials Research Society (MRS), and the Resnick Institute. Worldwide explorations for economic deposits of REEs and efforts to bring them into production have increased substantially since 2000. More than 400 rare-earth projects were in progress during 2012, including many projects in advanced stages of explora- tion, meaning that the deposit sizes and REE concentrations were announced based on detailed drilling. One important aspect in the development of a property for REE mining is the cost and complexity of processing the REE ores. Recovery of REEs can be complex because they occur in minerals as a group of similar elements, and at many deposits the REEs are hosted within more than one mineral. Not only do REE-rich minerals need to be concentrated, but the actual elements must be separated from each other, usually as oxide compounds (for example, ). The success and timeliness of rare-earth mining projects, and the rare-earth elements industry in general, is difficult to predict and will be continuously monitored and studied by the USGS.

References Did you know.... Lide, D.R., ed., 2004, Abundance of elements in the Earth’s crust and In the 1940s, as part of the Manhattan Project that in the sea, in sec. 14 of CRC handbook of physics and chemistry— created the nuclear bomb, Frank Spedding and others in the A ready-reference book of chemical and physical data (85th edition): United States developed chemical procedures Boca Raton, Fla., CRC Press, p. 17 [table]. that could separate and purify individual REEs. This method Long, K.R., Van Gosen, B.S., Foley, N.K., and Cordier, Daniel, was first used to separate plutonium-239 and neptunium 2010, The principal rare earth elements deposits of the United from uranium, thorium, and actinium in materials generated States—A summary of domestic deposits and a global perspective: by nuclear reactors. U.S. Geological Survey Scientific Investigations Report 2010 –5220, 96 p. [Also available at http://pubs.usgs.gov/sir/2010/5220/.] National Research Council, 2008, Minerals, critical minerals, and the How Do We Ensure Adequate Supplies of U.S. economy: Washington, D.C., National Academies Press, 264 p. [Also available at http://www.nap.edu/openbook.php?record_id=12034.] Rare-Earth Elements for the Future? Global REE resources are estimated to be 110 million For More Information metric tons of rare-earth oxide, which primarily occur, in On production and consumption of rare-earth elements: descending order, in China, Russia, the United States, India, and http://minerals.usgs.gov/minerals/pubs/commodity/rare_earths/ Australia. Exploration for additional REE deposits is ongoing; On historical statistics of rare-earth elements: therefore, the world’s known in-the-ground resources (endow- http://minerals.usgs.gov/ds/2005/140/ ment) of REEs are likely to increase. Despite many known REE On end use and recycling of rare-earth elements: deposits, the global supply of REEs is limited by the cost and http://pubs.usgs.gov/sir/2011/5094/ complexity of exploring REE deposits and developing REE The USGS Mineral Resources Program is the sole Federal provider mines, including REE extraction and separation facilities. These of research and information on rare-earth elements and other nonfuel factors are discussed in USGS Scientific Investigations Report mineral resources. For more information, please contact: 2010 –5220 (available at http://pubs.usgs.gov/sir/2010/5220/). Mineral Resources In addition to bringing more REE deposits into produc- Program Coordinator Telephone: 703-648-6100 tion, other methods may help offset REE supply restrictions. U.S. Geological Survey Fax: 703-648-6057 Examples include new efforts to recycle REEs, research to find 913 National Center E-mail: [email protected] substitute materials for REEs, and efforts to recover REEs as Reston, VA 20192 Home page: http://minerals.usgs.gov coproducts of mineral deposits. These efforts may eventually Text prepared by Bradley S. Van Gosen, Philip L. Verplanck, offset some of the demand for REEs. Keith R. Long, Joseph Gambogi, and Robert R. Seal II.

ISSN 2327– 6932 (online) http://dx.doi.org/10.3133/fs20143078